The death of four members of a family in south Mumbai last month was caused by zinc phosphide, a chemical commonly used in rat poison, and not by consumption of watermelon, as initially suspected, PTI reported on Thursday, quoting officials.The matter came to light in April when a Muslim family, consisting of husband, wife and their two daughters, died due to suspected food poisoning.Earlier, Deputy Commissioner of Police (Zone 1) Praveen Munde had said that investigation into the deaths was underway and food and body samples had been collected for examination after post-mortem.In a self-recorded video statement released last month, Munde said the family had invited relatives for a meal at their residence on April 25.He said, “A report of unnatural death has been lodged at JJ Marg police station. Four members of a Muslim family – husband, wife and their two daughters – died. On April 25, he called some relatives to his home and had dinner with them. After the meal, around 10-10.30 pm, the relatives left.”Munde said, “The family ate watermelon at around 1-1.30 in the night. At around 5-6 in the morning, they started complaining of vomiting and diarrhoea. They were taken to a nearby hospital and all four of them died yesterday.”He had also said that post-mortem was conducted and samples were collected as part of the investigation.He had said, “Postmortem was conducted and food samples and samples were also taken from his body. Further investigation is underway.”Earlier on Wednesday, officials said post-mortem had been conducted and the viscera of the deceased had been preserved for chemical analysis. As part of the investigation, the microbiology department of JJ Hospital had submitted a preliminary report to the police stating that no bacterial infection was found in the victims.An official had said, “As per reports, no bacterial infection has been found in the bodies of the victims so far. No bacteria were found in their blood.”Officials said the exact cause of death will be determined after the forensic science laboratory submits its final report. “The report will also clarify whether there was anything poisonous in any of the food items consumed by the family members during the day,” the official said.